Wednesday, June 18, 2008

Review of Scientific Literature on Yoga I

Earliest Scientific Studies

The earliest scientific studies on yoga were conducted by Swami Kuvalayananda (1925). He reported the radiological and pressure changes in the viscera related to the practice of Uddiyana Bandha and Nauli. Later, a pupil of his (K.T. Behanan) carried out a systematic study (Behanan, 1937), on the oxygen consumption during pranayamas and reported an increase in the oxygen consumed, ranging from 12 to 25%, during the practice of Ujjayi, Kapalabhati, and Bhastrika pranayamas.

The ability of certain yogis to exert voluntary control over the heart aroused a spate of interest among scientists. The earliest study (Brosse, 1946), showed a decrease in magnitude of heart potentials and pulse wave, approximately to zero, for several seconds before returning to normal.

Later researchers (Satyanarayanmurthy and Shastry, 1958; Wenger et al., 1961; Ananda and Chhinna, 1961), reported brief periods of weakening or disappearance of heart and radial pulse sounds, associated with retention of breath and considerable muscular tension in the abdomen and thorax, with a closed glottis (i.e., an exaggerated Valsalva maneuver in some form). In another study (Kothari et al., 1973), an interesting and different type of yogic control over the heart was reported. After 29 hours in an underground pit, the normal ECG of the subject was replaced by a straight line, which persisted for the next 5 days. Electrical activity returned about half an hour before the pit was scheduled to be opened. The authors did not give any definite explanation for this phenomenon. Another effect of yogic practice which has been of interest to scientists, is the ability to lower the metabolic requirements, enabling the yoga practitioners to stay in an air tight pit for longer periods than control (non-yoga practitioners) subjects, without signs of distress (Anand et al., 1961).

In the study of Karambelkar et al. (1968), it was found that the oxygen consumption of four subjects in an airtight pit was less than the value predicted on the basis of their basal oxygen consumption. For the subjects with training in pranayama, the reduction in oxygen consumption, was less than for the others. The authors speculated that this might indicate that pranayama practice provides acclimatization to higher carbon dioxide content in the inspired air.

Around 1960, Maharishi Mahesh Yogi introduced Transcendental Meditation (TM) to the western world. The TM technique is taught as a simple practice, and provides an opportunity for scientific research. Robert Keith Wallace in his doctoral thesis (Wallace, 1970) and subsequent published researches (Wallace, 1970, Wallace et al., 1971), reported definite effects in terms of reduced metabolic rate, changes in blood chemistry, increased skin resistance, and a consistent pattern of changes in the EEG.